Viscous fluid clutch

ABSTRACT

A viscous fluid clutch including relatively rotatable first and second drive members having a fluid shear space therebetween and which are cooperable with a fluid medium in the shear space to provide a shear-type fluid drive therebetween, an annular reservoir for at times storing the fluid medium, a temperatureresponsive valve for controlling the flow of the fluid medium from the annular reservoir through an inlet port to the fluid shear space, continually open outlet ports and cooperating pump elements or wipers for forcing the fluid medium from the fluid shear space to the reservoir, and an annular cushion member mounted on one of the drive members, radially outwardly of the oppositely disposed ridge and groove shear space elements, between either radially extending or parallel tapered thrust faces of the clutch and housing members for improving the bearing characteristics and/or cushioning the impact therebetween under &#39;&#39;&#39;&#39;wobble&#39;&#39;&#39;&#39; conditions.

ilnited States Patent lnventor [H1 9,62%,udi

. Primary Examiner-Allan D. l-ierrmann.

Attorneys-Warren E. Finlten, A. M. Heiter and John P.

Moran ABSTRACT: A viscous fluid clutch including relativelyrotatablefirst and second drive members having a fluid shear spacetherebetween and which are cooperable with a fluid medium in the shearspace to provide a shear-type fluid drive therebetween, an annularreservoir for at times storing the fluid medium, atemperature-responsive valve for controlling the flow of the fluidmedium from the annular reservoir through an inlet port to the fluidshear space, continually open outlet ports and cooperating pump elementsor wipers for forcing the fluid medium from the fluid shear space to thereservoir, and an annular cushion member mounted on one of the drivemembers, radially outwardlly of the oppositely disposed ridge and grooveshear space elements, between either radially extending or paralleltapered thrust faces of the clutch and housing members for improving thehearing characteristics and/or cushioning the impact therehetween under.wobble" conditions.

[72] John N. Snodgrass Miamisburg, Ohio [21] Appl. No. 32,265 [22]Filed- Apr. 27,1970 [45] Patented Dec. 21, 19711 [73] Assignee GeneralMotors Corporation Detroit, Mich.

[54] VISCOUS FLUID CLUTCH 10 Claims, 9 Drawing Figs.

[52] U.S. Cl 192/58 9, 192/82 T [51] Int. Cl Fl6d 315/00 [50] Field oliSearch 192/58 A, 58 B, 58 C, 82 T [56] Retcrences Cited UNiTED STATESPATENTS 3,144,922 8/1964 Weir 192/58 B 3,259,221 7/1966 Godfrey 192/58 B2,902,127 9/1959 Hardy 192/58 8 PATENTEU nice? m 3,628,641

9 I NVEN TOR,

BY flvhnN; Snodgmss TEMPERATURE 2 Z F A N SPEED ATTORNEY VISCQUS FLUIDCLUTCH This invention relates generally to variable speed drive devices,and more particularly, to a viscous fluid drive adapted to drive anaccessory device, such as a cooling fan, for an internal combustionengine.

Vehicle cooling farts are generally belt driven from the enginecrankshaft, and are operable at a fixed speed ratio with respect to thevehicle engine. It has been found desirable to vary the speed ratio ofthe fan with respect to the engine speed so that at low engine speed thefan will be running at a relatively high speed for maximum cooling andas the speed of the engine increases, such as when the vehicle isrunning in direct drive at road speeds, the ram air cooling effect onthe engine is increased and the necessity for fan cooling is diminished.The resultant lower fan speed eliminates excessive fan noise whichotherwise could be disturbing to the occupants of the vehicle.

The device disclosed herein relates to an engine cooling fan mechanismwherein a viscous fluid, shear-type clutch is utilized to transmit powerfrom the vehicle engine to the fan blade assembly.

An object of the invention is to provide improved means for improvingthe bearing characteristics between the clutch and housing members underwobble" conditions.

Another object of the invention is to provide improved meansintermediate the thrust faces of the clutch and housing members, eitherfreely mounted therebetween or secured for rotation with one of themembers, for decreasing wear on the members.

A specific object of the invention is to provide a viscous shear fandrive having a housing including a rear wall, a front wall, a dividerwall therebetween, an operating or working chamber formed between therear and divider walls for receiving a clutch plate in viscous sheardrive relation with the housing, an annular reservoir formed between thedivider and front walls, continuously open outlet ports formed in thedivider wall and cooperating pump or dam means for forcing the fluidfrom the reservoir and through the outlets into the operating chamber, atemperature-controlled inlet port formed in the divider wall between theoperating chamber and the reservoir, and a washer member mounted betweenand secured to one of opposing parallel thrust faces of the rear walland the clutch plate radially outwardly of the ridge and groove elementswhich produce the viscous shear drive relationship.

A more specific object of the invention is to provide such a viscousshear fan drive, wherein the opposing parallel thrust faces of the rearwall and the clutch plate are tapered, causing the intermediate washermember to flex under wobble conditions, thereby cushioning the impacttherebetween and, consequently reducing the load on the water pump.

These and other objects and advantages will become apparent whenreference is made to the following description and the accompanyingdrawings, wherein:

FIG. 1 is a fragmentary side elevational view of a radiator and enginehaving a viscous fluid clutch-driven cooling fan associated therewith;

FIG. 2 is an enlarged fragmentary cross-sectional view of a viscousfluid, shear-type clutch embodying the invention;

FIG. 3 is a cross-sectional view taken on the plane of line 33 of FIG.2, as if FIG. 2 were a complete and full round view, and looking in thedirection of the arrows;

FIGS. 4 and 5 are fragmentary cross-sectional views taken on the planesof lines 44 and 5-5, respectively, of FIG. 3, and looking in thedirections of the arrows;

FIG. 6 is a fragmentary cross-sectional view taken on the plane of line6-6 of FIG. 5, and looking in the direction of the arrows;

FIGS. 7 and 8 illustrate an alternate embodiment of a portion of theFIG. 5 structure; and

FIG. 9 is a graph illustrating a characteristic of the invention.

Referring to the drawings in greater detail, FIG. I illustrates anengine 10 having a viscous fluid clutch l2 and a pulley 11 mounted on adrive shaft 13 extending from the conventional water pump 14, the pulley11 being rotated by a V-belt 15 connected to the crankshaft (not shown)for driving a cooling fan to secured to the clutch 112. The fluid clutchl2 and the cooling fan 16 are located between the engine 10 and aradiator it}. The usual conduits 20 and associated hoses 22 commuhousing23.'Cooling fins and 3b are formed on the outer.

surfaces of the rear wall member 24 and the cover member 30,respectively. A second annular recess 33 is formed radially inward ofthe outer periphery of the annular recess 341. A divider wall isconfined adjacent its outer edge in the second annular recess 38 by thecover member 30. A seal d2 is compressed in an annular groove 43 formedin the rear wall member 24 intermediate the outer edges of the annularrecesses 34 and 38. A third annular deeper recess 4d is formed in therear wall member 24 radially inward of the second annular recess 38. Aclutch plate 46 is secured at its center by any suitable means to thedrive shaft 13, the outer peripheral portion thereof being freelylocated in an operating or working chamber as formed by the thirdannular recess 4%.

Adjacent portions of the clutch plate as and the rear wall member 241are provided with torque-transmitting elements consisting of cooperatingannular ridge and groove elements 50 and 52, respectively, with anintervening fluid shear space 54 therebetween to accommodate a viscousfluid as a torquetransmitting medium.

Referring now to FIG. 3, it may be noted that the clutch plate 46further includes a plurality of equispaced openings 55 formed therein ata point radially inward from the ridge and grove elements 50 and 52. Apair of oppositely disposed smaller openings 56 are formed in the clutchplate 46 adjacent the outermost edge thereof, one of which isillustrated as being radially aligned with one of the larger openings55, but such need not be the case. A pair of radial grooves, such as Vshaped grooves 57 (FIGS. 3 and ll), are formed in the clutch plate 46across the ridges 5t) and terminating at the openings 56. The grooves 57assist in the process of removing the fluid medium for the workingchamber M.

It may be noted in FIG. 2 that the front wall or cover member 30includes an annular bend intermediate the centers and peripheral edgesthereof which forms an annular reservoir 58 with the divider wall 40.One or more pump outlet openings 60 are formed through the divider wall40 circumferentially adjacent pump or dam elements 62 formed on thedivider wall dill, and at substantially the same radial distance fromthe center of the clutch 12 as the outer clutch plate openings 56. Thepump outlet openings 60 communicate between the operating chamber db andthe annular reservoir 53 and are substantially the same diameter as theclutch plate openings 56. The pump or darn elements 62 may consist of acircular boss formed on the divider wall W by any suitable means, suchas stamping, or it may be a rectangular-shaped or other-shaped membersecured to the divider wall 40, such as by welding. It is to beunderstood that, in some applications, one outlet and one pump elementmay be sufficient, while other applications may require two such pumpingarrangements. In the latter instance, one of the outlet openings 60 mayat times be closed by an internal bimetallic thermostatic valve (notshown).

It may be noted in FIGS. 2 and 5 that a wear-cushion member 64 islocated between the opposing thrust faces 65 and 66 of the clutch plateas and the rear wall member 24, respectively, radially outwardly of theridge and groove elements 50 and 52. The wear-cushion member 641 may besecured in any suitable manner for rotation with the clutch plate 46,or, as illustrated in FIGS 5 and t5, the cushion 64 may include one ormore protrusions 67 formed on its outer periphery for insertion incooperating longitudinal slots 68 formed in the wall of the recess 44 inthe rear wall member 24.

As further illustrated in FIG. 7, the opposing faces 65 and 66 of theclutch plate 46 and the rear wall member 24, respectively, may beparallel tapered so that, under any wobble conditions, the clutch face65 will first contact one side of the wear-cushion 64 at the radiallyoutermost portion thereof, while the rear wall face 66 will firstcontact the outer side of the wear-cushion 64 at the radially innermostportion thereof for a purpose to be described.

One or more inlet ports 70 are also formed in the divider wall 40,communicating between the annular reservoir 58 and the working chamber48 radially inward of the pump elements 62 and the pump outlet openings60. The inlet port 70 is at times closed off by a valve member 72, whichmay be responsive to temperature changes or to centrifugal force. Thevalve member 72 is illustrated as being secured in any suitable mannerto a reduced diameter portion 76 of a center pin or shaft 78, which isrotatably mounted in a central opening 80 formed in the front wall orcover member 30. A seal ring 82 may be mounted in an annular groove 84formed in the pin 78 within the central opening 80 to prevent leakagetherepast. A helically wound, bimetallic thermostatic valve controlelement 86 is provided with an inwardly extending end portion 88 whichis mounted in a transverse slot 90 formed in the pin '78. An outwardlyextending end portion 92 of the bimetallic element 86 is secured to apost 94. With this arrangement, a change in ambient temperature eitherwinds or unwinds the bimetallic element 86, resulting in rotation of thepin 78 and the valve member 72.

OPERATION So long as the vehicle engine (FIG. 1) is in operation, thedrive shaft 13 and the associated clutch plate 46 (FIG. 2) will bedriven by the pulley l1 operatively connected via the belt 15 to thecrankshaft (not shown) at an appropriate speed ratio with respect toengine speed. The initial position of the temperature-responsive valvemember 72 will be closed across the inlet port or opening 70 in thedivider wall 40, and will remain closed so long as the engine is cold,thus preventing any flow of fluid from the annular reservoir 58 into theworking chamber 48. Since at least one pump outlet opening 60 is alwaysopen, providing continuous communication between the working chamber 48and the annular reservoir 58, fluid from the working chamber 48 will bepumped therethrough by virtue of the pump elements 62 serving as dams orwipers, forcing the fluid to flow into the respective pump outletopenings 60 and, thence, into the annular reservoir 58. A continualsupply of fluid is made available to the wiper elements 62 by virtue ofthe openings 56 formed in the clutch plate 46. The openings 56 are fedby fluid from the radial grooves 57 under the action of centrifugalforce and the effect of suction created by the pumping action of thewiper elements 62 and the outlets 60.

The total volume of fluid is such that when working chamber 48 issubstantially empty, i.e., at a level designated by broken line E, FIG.2, at the outermost edge of the openings 56, the fluid in the annularreservoir 58 will be held under the action of centrifugal force in theouter annular portion of the reservoir 58 with an inner from liquidlevel A," FIG. 2, the head resulting from the fluid height A" to E beingoffset by the force generated by the pumping action of the pump elements62 on the fluid remaining in the working chamber 48, to prevent anyflow-back through the pump outlet openings 60. Under this condition,commonly known as the disengaged mode, the slip between the clutch plate46 and the housing 23 is greatest, and fan 16 speed is correspondinglylow, as represented by the curve A in FIG. 9.

As the ambient temperature increases due to the warmup of the radiatorand engine, the bimetallic thermostatic valve control element 86 willbegin to wind up and, since it is restrained at its outer end portion 92by the post 94, its inner end portion 88 will rotate the cooperativelyconnected pin 78 and the valve member 72, progressively uncovering theinlet ports 70 in the divider wall 40, as will be described. As aresult, fluid will flow through the inlet ports 70 back into the workingchamber 48, generally progressively increasing the volume therein withincreasing temperature. More specifically, as the fluid is admittedthrough the inlet ports 70 by the temperature-controlled valve element72, it will first be projected radially outwardly between the dividerwall 40 and the adjacent face of the clutch plate 46. It is believed tobegin to fill the peripheral shear space between the outer edge of theclutch plate 46 and the wall of the annular recess 44, while fillingradially inwardly between the divider wall 40 and the adjacent face ofthe clutch plate 46. Once the fluid attains a level radially within theouter edge of the openings 55 formed in the clutch plate 46, it willspill through the openings 55 into the shear space 54.

It is felt that the spaces between the sides of the wearcushion member64 and the respective adjacent faces 65 and 66 of the clutch plate 46and the rear wall member 24 may be filled with the fluid flowing eitherinwardly from the peripheral shear space between the outer edge of theclutch plate 46 and the wall of the annular recess 44, or outwardly fromthe ridge and groove fluid shear space 54, or some combination thereof.

Throughout the above, the volumeof flow through the continually openpump outlet ports 60 remain s substantially constant, being influencedby the rotary speed of the clutch plate 46, and the working chamber 48is filled in the manner just described until the inner annular levels inboth the working chamber 48 and the annular reservoir 58 are at thelevel designated by C (FIG. 2), after which the fan 16 speed will remainat its highest constant speed, as represented by the corresponding curveC of FIG. 9.

It is apparent that, as the viscous fluid is admitted to the workingchamber 48 with increased temperature, filling the fluid shear space 54between the oppositely disposed spaced ridge and groove elements and 52,the shear-type fluid drive there between will be influenced, andslip-speed," or the difference between the speed of the clutch plate 46and that of the housing 23, will decrease, with the fan 16 speedprogressively increasing, as indicated by curve B' in FIG. 9. So long asthe inlet ports 70 in the divider wall 40 remain open, a fluidcirculation process will prevail, i.e., the rotating pump or darnelements 62 will continue to promote the flow of fluid form the workingchamber 48 through the pump outlet openings 60 to the annular reservoir58 from whence it will continually return to the working chamber 48 viathe variably opening inlet ports 70.

As indicated, when the cooling requirements are at a maximum, thetemperature-responsive valve member 72 will have rotated completely pastthe inlet openings 70, permitting the fluid in the chamber 48 and theannular reservoir 58 to reach a point of equilibrium, i.e., liquid levelC" in FIG. 2, causing the relatively rotatable drive members 46 and 24to operate at minimum slip-speed and thereby effecting a maximum coolingfunction, inasmuch as the fan 16 is secured to the outer portion of therear wall member 24 of the housing 23 (FIG. 1 So long as the inlet ports70 remain fully open, the circulation process described above willmaintain the level C illustrated in FIG. 2.

Throughout the above-described cycle there are times when the reactionsof the various moving components will result in wobble" of the clutchplate 46 relative to the rear wall member 24. Heretofore, in order toforestall the ridges 50 from contacting the grooves 52, and resulting inwear therebetween which adversely affects the shear drivecharacteristic, care has been exercised to assure that the thrust face65 of the clutch plate 46 will contact the thrust face 66 of the rearwall 24 before any ridge 50 can contact its adjacent groove 52. This,however, has resulted in excessive wear occurring on either the clutchplate face 65 or the rear wall face 66 and the eventual contact betweenthe juxtapositioned ridg Sti and the groove 52 elements. a

It is a feature of the invention to provide a wear-cushion member 64formed of a high-quality wear-resistant steel composition or othersuitable material intermediate the faces 65 and 66, the latter facesbeing spaced apart at assembly as required to accommodate the insertionof the wear-cushion member 64, the latter member serving as a cushion orbuffer and also as a bearing member therebetween which greatly minimizesthe wear on either of the relatively rotating drive members.

If desired, as indicated above, the wear-cushion or hearing member 64may be secured in any suitable manner to any convenient portion of theclutch plate 46. Also, if desired, the member 64 may be mounted forrotation with the rear wall 24 via interconnected protrusion and slotelements 67 and 66, respectively, (MG. 6). formed on the outer peripheryof the wear-cushion 64 and the cylindrical wall of the recess 44. As maybe noted in MG. 6, the protrusions 67 are freely fitted in the slots 66in order that the wear-cushion member 64 may move axially relative tothe housing 23 and the clutch plate 46.

The overall space provided between the clutch plate 46 and i the wall 24is such that, after the insertion of the wear-cushion member 64 in placein the housing 23, the space remaining between the wear-cushion 64 andthe clutch plate 46 will serve as an additional shear-drive space,supplementing the shear-drive provided by the shear space 54 between theridge and groove elements 50 and 52. Allowance in the overall spacebetween the faces 65 and 66 of the clutch plate 46 and the rear wall 24,respectively, is also made for a film of fluid between the face 66 ofthe rear wall 24 and the adjacent face of the wear-cushion member 64.Such a film of fluid serves to cushion any impact shock that might occurbetween the relatively rotating members, under wobble conditions orother pivotal or axial movements therebetween.

A supply of fluid is assured by virtue of the slots 68 serving as apassage for the fluid which is pumped therethrough by the relativerotation between the outer edge of the clutch plate 46 and the adjacentwall of the housing 24. Such pumping action continually forces the fluidradially inwardly between the wall 24 and the wear-cushion member 64 andover the inner peripheral edge of the latter. If necessary, the lattermay include circumferential openings or notches formed at spacedintervals around the inner periphery thereof, to aid the fluid which isbeing forced inwardly, as described, to spill past the radiallyoutermost ridge member 50 into the space between the clutch plate 46 andthe cushion member 64. in view of the flowpath just described, fluidwill not remain confined between the cushion member 64 and the rear wall24 and thus serves as a pressure means forcing the cushion member 64away from the wall 24 to contact the clutch plate 46 or to approach soclose thereto that the desired shear-drive relationship is varied. ifdesired, pockets may be formed in the wall 24 adjacent the outer edge ofthe wear-cushion 64 for receiving the fluid.

it has been determined that with the longitudinal slots 66 formed in thewall of the recess 44 in the rear wall member 24 and located in apredetermined radial relationship with the outlet openings 60 and thepump or dam elements 62, whether or n ot the opposing faces 65 and 66 ofthe clutch plate 46 and the rear wall 24, respectively, are spaced farenough apart to accommodate the inclusion of the wear-cushion member 64,during a cold start" operation, the time required of the fluid to bepumped out of the working chamber 46, in order to eliminate fan noise,is substantially shortened, as compared to the time required when thelongitudinal slots 68 are not employed.

Another embodiment is illustrated in FIG. 7, wherein the respectiveclutch plate and wall member faces 65 and 66 are formed to slopeparallel to one another. In this arrangement, the intermediatewear-cushion member 64 is forced to flex under pivotal or axial movableconditions, in the manner illustrated in the exaggerated wobblecondition view of FlG. 8.

Such flexing serves to further cushion the impact between the clutchplate 46 and the flexible member 64 and between the latter and the rearwall 24, thereby reducing the resultant intermittent increased loads onthe water pump i4 (lFlG. ll) through the drive shaft 113, while reducingwear on the contacting members. The parallel relationship betweenopposing faces 65 and 66 may be in the reverse direction, so that theflexing of the wear-cushion is the reverse of that illustrated in H6.63.

it should be apparent that the invention provides improved means forminimizing wear and cushioning the impact shock between the variousrelatively rotatable components of the clutch H2 heretofore encounteredunder wobble conditions, thereby increasing the operational life of theclutch l2 and of the associated water pump 114.

it should be further apparent that one embodiment of the inventionprovides improved means for cushioning any impact between relativelyrotatable and axially or pivotally movable drive members, therebyreducing the load on the associated water pump.

While several embodiments of the invention have been shown anddescribed, other modifications thereof are possible.

1 claim:

ll. A viscous fluid clutch comprising first and second relativelyrotatable drive means, said first drive means having an annularoperating chamber and a reservoir chamber, fluid shear drive meansformed on oppositely disposed annular portions of said first and seconddrive means located in said operating chamber forming a shear spacetherebetween and operable with a fluid to provide a shear-type fluiddrive between said first and second drive means, said operating chamberhaving outlet opening means at an outer portion and inlet opening meansat an inner portion, pump means on one of said drive means to pump fluidfrom said operating chamber through said outlet opening means to saidreservoir chamber, and an annular wear-cushion member mounted radiallyoutwardly of said fluid shear drive means intermediate second oppositelydisposed annular portions of said first and second drive means andoperatively connected to one of said first and second drive means so asto be rotatable therewith and axially movable relative thereto forminimizing wear on the other of said first and second drive means andcushioning the impact therebetween during relative operational wobble ofsaid first and second drive means.

2. A viscous fluid clutch comprising; first and second relativelyrotatable drive means, said first drive means having an annularoperating chamber and a reservoir chamber, said second drive means beingrotatably mounted in said operating chamber, a plurality of annularridges formed on one of said first and second drive means and aplurality of cooperating annular grooves formed on the other of saidfirst and second drive means in said operating chamber, said annularridges and grooves forming a shear space ther'ebetween the operable witha fluid to provide a shear-type fluid drive between said first andsecond drive means, said operating chamber having an outlet openingmeans at an outer portion and inlet opening means at an inner portion,pump means on one of said drive means to pump fluid from said operatingchamber through said outlet opening means to said reservoir chamber, anda plurality of longitudinal slots formed at spaced intervals in thesurface of said first drive means around the outer periphery of saidannular operating chamber and coordinated with the locations of saidoutlet opening means and said pump means for aiding said pump means toquickly pump said fluid from said operating chamber through said outletopening means during a cold start operation.

3. The clutch described in claim ll, wherein said wearcushion member isconnected for rotation with said first drive means.

4. The clutch described in claim ll, wherein said wearcushion member isconnected for rotation with said second drive means.

5. A viscous fluid clutch comprising first and second relativelyrotatable drive members; and first drive member including a first wall,a second wall, a divider wall sealed between said first and secondwalls, providing a working chamber between said divider and second wallsand a second chamber between said first and divider walls, and aplurality of longitudinal slots formed therein adjacent said workingchamber; fluid shear drive means formed on each of said first and seconddrive members, at first oppositely disposed annular portions thereof insaid working chamber forming a shear space therebetween and a pluralityoperable with a fluid medium to provide a shear-type fluid drivetherebetween; first opening means in said divider wall for providingcommunication from said working chamber to said second chamber; pumpmeans on one of said drive members for causing said fluid medium to flowform said working chamber through said first opening means to saidsecond chamber; second opening means formed in said divider wall forcommunicating said fluid medium from said second chamber to said workingchamber; a wear-cushion member mounted radially outwardly of said fluidshear drive means intermediate second oppositely disposed annularportions of said first and second drive means for minimizing wear onsaid first and second drive means and preventing contact between saidfluid shear drive means during relative operational wobble of said firstand second drive means; plurality of protrusions formed on saidwear-cushion member for being slidably mounted in said longitudinalslots to cause said wear-cushion member to rotate with said first drivemember and to permit said wear-cushion member to slide axially relativeto said first drive member and thereby permit said fluid medium toprovide a fluid shear drive relationship between said wear-cushionmember and said second drive member and to provide a cushioning meansbetween said wear-cushion member and said first drive member.

6 A viscous fluid clutch comprising relatively rotatable housing andclutch plate members, said housing member including front and rear wallsand defining a fluid cavity therebetween, a divider wall sealed betweensaid front and rear walls in said fluid cavity and dividing said fluidcavity to first and second chambers, said clutch plate member beingrotatable in said first chamber, said clutch plate member and said rearwall having opposed spaced annular parallel ridge and groove surfacesformed thereon defining a fluid shear space therebetween and cooperablewith a fluid medium in said shear space to provide a shear-type fluiddrive therebetween, a first opening formed in said divider wall forproviding communication in said first chamber adjacent said firstopening for causing said fluid medium to flow through said first openingfor varying the volume of said fluid medium in said shear spwe to varythe torque transmitted between said housing and clutch plate members, asecond opening formed in said divider wall for at times communicatingsaid fluid medium for said second chamber to said first chamber, valvemeans for controlling the flow of said fluid medium through said secondopening to further vary the torque transmitted between said housing andclutch plate members, an annular wear-cushion member secured forrotation with an axial movement relative to said housing member andadjacent opposing faces of said clutch plate and housing members, saidfaces being located radially outwardly of said opposed spaced annularparallel ridge and groove surfaces.

7. The viscous fluid clutch described in claim 6, and bimetallicthermostat means for actuating said valve means.

8. The viscous fluid clutch described in claim 6, wherein said faces areparallel to one another and extend radially outwardly from the axis ofsaid viscous fluid clutch.

9. The viscous fluid clutch described in claim 6, wherein said face onsaid clutch plate includes a first portion closely adjacent an outerannular portion of said wear-cushion member and an inwardly extendingportion tapering away from said wear-cushion member, and said face onsaid housing includes a first portion closely adjacent an inner annularportion of said wear-cushion member of the side 0 posite said outerannular portion and an outwardly exten mg portion tapering away fromsaid wear-cushion member, said wearcushion member being caused to flexintermediate and housing and clutch plate members during relativepivotal movement of one of said housing and clutch plate members,thereby cushioning the impact therebetween.

10. The viscous fluid clutch described in claim 6, wherein said face onsaid clutch plate a first portion closely adjacent a first annularportion of said wear-cushion member and a second portion tapering awayfrom said wear-cushion member and a second portion tapering away fromsaid wear-cushion member, ans said face on said housing includes a firstportion closely adjacent a second annular portion of said wearcushionmember on the side opposite said first annular portion and a secondportion tapering away from said wear-cushion member, said wear-cushionmember being caused to flex intermediate said housing and clutch platemembers during relative pivotal movement of one of said housing andclutch plate members, thereby cushioning the impact therebetween.

1. A viscous fluid clutch comprising first and second relativelyrotatable drive means, said first drive means having an annularoperating chamber and a reservoir chamber, fluid shear drive meansformed on oppositely disposed annular portions of said first and secOnddrive means located in said operating chamber forming a shear spacetherebetween and operable with a fluid to provide a shear-type fluiddrive between said first and second drive means, said operating chamberhaving outlet opening means at an outer portion and inlet opening meansat an inner portion, pump means on one of said drive means to pump fluidfrom said operating chamber through said outlet opening means to saidreservoir chamber, and an annular wear-cushion member mounted radiallyoutwardly of said fluid shear drive means intermediate second oppositelydisposed annular portions of said first and second drive means andoperatively connected to one of said first and second drive means so asto be rotatable therewith and axially movable relative thereto forminimizing wear on the other of said first and second drive means andcushioning the impact therebetween during relative operational wobble ofsaid first and second drive means.
 2. A viscous fluid clutch comprisingfirst and second relatively rotatable drive means, said first drivemeans having an annular operating chamber and a reservoir chamber, saidsecond drive means being rotatably mounted in said operating chamber, aplurality of annular ridges formed on one of said first and second drivemeans and a plurality of cooperating annular grooves formed on the otherof said first and second drive means in said operating chamber, saidannular ridges and grooves forming a shear space therebetween theoperable with a fluid to provide a shear-type fluid drive between saidfirst and second drive means, said operating chamber having an outletopening means at an outer portion and inlet opening means at an innerportion, pump means on one of said drive means to pump fluid from saidoperating chamber through said outlet opening means to said reservoirchamber, and a plurality of longitudinal slots formed at spacedintervals in the surface of said first drive means around the outerperiphery of said annular operating chamber and coordinated with thelocations of said outlet opening means and said pump means for aidingsaid pump means to quickly pump said fluid from said operating chamberthrough said outlet opening means during a cold start operation.
 3. Theclutch described in claim 1, wherein said wear-cushion member isconnected for rotation with said first drive means.
 4. The clutchdescribed in claim 1, wherein said wear-cushion member is connected forrotation with said second drive means.
 5. A viscous fluid clutchcomprising first and second relatively rotatable drive members; andfirst drive member including a first wall, a second wall, a divider wallsealed between said first and second walls, providing a working chamberbetween said divider and second walls and a second chamber between saidfirst and divider walls, and a plurality of longitudinal slots formedtherein adjacent said working chamber; fluid shear drive means formed oneach of said first and second drive members, at first oppositelydisposed annular portions thereof in said working chamber forming ashear space therebetween and a plurality operable with a fluid medium toprovide a shear-type fluid drive therebetween; first opening means insaid divider wall for providing communication from said working chamberto said second chamber; pump means on one of said drive members forcausing said fluid medium to flow form said working chamber through saidfirst opening means to said second chamber; second opening means formedin said divider wall for communicating said fluid medium from saidsecond chamber to said working chamber; a wear-cushion member mountedradially outwardly of said fluid shear drive means intermediate secondoppositely disposed annular portions of said first and second drivemeans for minimizing wear on said first and second drive means andpreventing contact between said fluid shear drive means during relativeoperational wobble of said first and second drive means; plurality ofprotrusions formed on said wear-cushion memBer for being slidablymounted in said longitudinal slots to cause said wear-cushion member torotate with said first drive member and to permit said wear-cushionmember to slide axially relative to said first drive member and therebypermit said fluid medium to provide a fluid shear drive relationshipbetween said wear-cushion member and said second drive member and toprovide a cushioning means between said wear-cushion member and saidfirst drive member.
 6. A viscous fluid clutch comprising relativelyrotatable housing and clutch plate members, said housing memberincluding front and rear walls and defining a fluid cavity therebetween,a divider wall sealed between said front and rear walls in said fluidcavity and dividing said fluid cavity to first and second chambers, saidclutch plate member being rotatable in said first chamber, said clutchplate member and said rear wall having opposed spaced annular parallelridge and groove surfaces formed thereon defining a fluid shear spacetherebetween and cooperable with a fluid medium in said shear space toprovide a shear-type fluid drive therebetween, a first opening formed insaid divider wall for providing communication in said first chamberadjacent said first opening for causing said fluid medium to flowthrough said first opening for varying the volume of said fluid mediumin said shear space to vary the torque transmitted between said housingand clutch plate members, a second opening formed in said divider wallfor at times communicating said fluid medium for said second chamber tosaid first chamber, valve means for controlling the flow of said fluidmedium through said second opening to further vary the torquetransmitted between said housing and clutch plate members, an annularwear-cushion member secured for rotation with an axial movement relativeto said housing member and adjacent opposing faces of said clutch plateand housing members, said faces being located radially outwardly of saidopposed spaced annular parallel ridge and groove surfaces.
 7. Theviscous fluid clutch described in claim 6, and bimetallic thermostatmeans for actuating said valve means.
 8. The viscous fluid clutchdescribed in claim 6, wherein said faces are parallel to one another andextend radially outwardly from the axis of said viscous fluid clutch. 9.The viscous fluid clutch described in claim 6, wherein said face on saidclutch plate includes a first portion closely adjacent an outer annularportion of said wear-cushion member and an inwardly extending portiontapering away from said wear-cushion member, and said face on saidhousing includes a first portion closely adjacent an inner annularportion of said wear-cushion member of the side opposite said outerannular portion and an outwardly extending portion tapering away fromsaid wear-cushion member, said wear-cushion member being caused to flexintermediate and housing and clutch plate members during relativepivotal movement of one of said housing and clutch plate members,thereby cushioning the impact therebetween.
 10. The viscous fluid clutchdescribed in claim 6, wherein said face on said clutch plate a firstportion closely adjacent a first annular portion of said wear-cushionmember and a second portion tapering away from said wear-cushion memberand a second portion tapering away from said wear-cushion member, anssaid face on said housing includes a first portion closely adjacent asecond annular portion of said wear-cushion member on the side oppositesaid first annular portion and a second portion tapering away from saidwear-cushion member, said wear-cushion member being caused to flexintermediate said housing and clutch plate members during relativepivotal movement of one of said housing and clutch plate members,thereby cushioning the impact therebetween.